Process for producing polyphenylene ethers

ABSTRACT

Polyphenylene ethers of 5 microns or more in particle size which are useful for preparation of parts of electric devices are continuously produced according to oxidative polymerization of 2,6-disubstituted phenols by preparing a 15 to 35 % (by weight) solution of 2,6-disubstituted phenol in dimethylformamide or in a mixed solvent composed of toluene and methanol, subjecting the solution to polymerization in one zone while maintaining the reaction system in the state of a homogeneous solution, and transferring the polymerization liquid to another zone to complete the polymerization while allowing the resulting polymer to precipitate.

United States Patent Izawa et al.

PROCESS FOR PRODUCING POLYPHENYLENE ETHERS Inventors: Shinichi Izawa,Tokyo; Kunio Toyama, Kanagawa; Yoshiaki Sugawara, Kanagawa; TsutomuTanaka, Kanagawa; Hidehiro Okamoto, Kanagawa, all of Japan Assignee:Asahi-Dow Limited, Tokyo, Japan Filed: Dec. 6, 1971 Appl. No.: 205,375

Foreign Application Priority Data Dec. 8, 1970 Japan 45-108107 US. Cl.260/47 ET Int. Cl C08g 23/18 Field of Search 260/47 ET References CitedUNITED STATES PATENTS 2/1967 Hay 260/47 10/1968 Meijs et a1. 260/47Primary ExaminerMelvin Goldstein Attorney, Agent, or Firm-Cushman, Darby&

Cushman 57 ABSTRACT Polyphenylene ethers of 5 microns or more inparticle size which are useful for preparation of parts of electricdevices are continuously produced according to oxidative polymerizationof 2,6-disubstituted phenols by preparing a 15 to 35 (by weight)solution of 2,6- disubstituted phenol in dimethylformamide or in a mixedsolvent composed of toluene and methanol, subjecting the solution topolymerization in one zone while maintaining the reaction system in thestate of a homogeneous solution, and transferring the polymerizationliquid to another zone to complete the polymerization while allowing theresulting polymer to precipitate.

10 Claims, N0 Drawings Hay 260/47 PROCESS FOR PRODUCING POLYPI-IENYLENEETHERS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to a process for continuously producing polyphenyleneethers of 5 microns or more in particle size by oxidative polymerizationof 2,6- disubstituted phenols.

Polyphenylene ethers are useful as thermoplastic resins having favorablethermal, mechanical and electrical properties and excellent in suchchemical properties as alkali resistance, acid resistance, hot waterresistance and the like.

2. Description of the Prior Arts As to the production of polyphenyleneethers, many processes have heretofore been proposed. However,substantially all of these processes are carried out in a batch-wisemanner using a solvent which dissolves both the starting phenol which isa monomer and the product polyphenylene ether which is a polymer.Relative to the continuous production of polyphenylene ethers, BritishPatent 1,087,488 discloses a process in which a phenol in the form of ahomogeneous solution in toluene is polymerized by use of a column typetwo-stage polymerizer In said British patent, however, no mention ismade with respect to the after-treatment step and no example is shownexcept the case where the monomer concentration is about 70. BritishPatent 1,051,399 discloses such a technique that in order to recover apolymer from a homogeneous toluene solution of said polymer, anazeotropic mixture of toluene and methanol is added to thepolymerization solution to precipitate the polymer. Thus, said Britishpatent teaches that for the polymerization process, it is also animportant measure to simplify the recovery of the solvent toluene. Sofar as a homogeneous solution polymerization reaction is adopted, thepolymerization solution is necessarily increased in viscosity.Accordingly, it is substantially impossible to increase the monomerconcentration to more than 10 Further, a quite difficult technicalproblem is brought about in making continuous the step of recovering thepolymer by mixing the polymerization solution with a precipitant.Moreover, the particle size of the polymer obtained is not more than 5microns.

SUMMARY OF THE INVENTION The present invention is a process forproducing polyphenylene ethers having a particle size of 5 to 500microns. Polymers having such a large particle size can be quite easilyfiltered, washed and dried.

The present invention provides a process for producing polyphenyleneethers by the continuous polymerization of lo disubstituted phenolshaving such a high concentration as to 35 7: by weight.

In accordance with the present invention, there is provided a processfor producing polyphenylene ethers by subjecting a 2,6-disubstitutedphenol to oxidative polymerization using a molecular oxygen-containinggas in the presence of a catalyst, characterized in that theconcentration of the 2,6-disubstituted phenol in the wholepolymerization reaction mixture is made 15 to 35 by weight, and thepolymerization is effected in two different zones, using a medium whichcan not dissolve a polyphenylene ether having a specific viscosity of0.25 or more, but the phenol as well as the catalyst.

In the first zone, the polymerization is carried out while preventingthe precipitation of polyphenylene ether, while in the second zone, thepolymerization is carried out while permitting the precipitation ofpolyphenylene ether.

According to the present process, the continuous polymerization ofphenol has been made possible. This is not only because the medium issuitably selected so as to precipitate the polymer to the form ofparticles but also because the polymerization conditions at each stageare suitably controlled so as to obtain optimum particles.

For practice of the present process, there are required a firstpolymerizer in which the polymerization is proceeded while maintainingthe reaction mixture in the form of a homogeneous solution, and a secondpolmerizer in which stable particles of polyphenylene ether aredeposited. If necessary, a third polymerizer is provided to control thefinal properties of the polymer particles by aging. Each of thesepolymerizers may be subdivided into several polymerizers in order tocarry out more delicate control.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Materials The2,6-disubstituted phenol is a phenolic compound represented by thegeneral formula,

wherein R is a straight chain alkyl group having one to four carbonatoms; and R is a halogen atom, an alkoxy group having one to fourcarbon atoms or an alkyl group having one to four carbon atoms. Examplesof the above-mentioned compound include 2,6- dimethylphenol,2-methyl-6-ethylphenol, 2,6- diethylphenol, 2-ethyl-6-n-propylphenol,2-methyl-6- chlorophenol, 2-methyI-6-bromophenol, Z-methyl- 6-methoxyphenol, 2-methyl- 6-propoxyphenol, Z-methyl- 6-n-propylphenol,Z-methyl- 6-n-butylphenol, 2,6-di-npropylphenol and 2-ethyl-6-chlorophenol.

Examples of the oxidative polymerization catalyst usable in the presentprocess are catalysts comprising the combinations of cuprous salts andtertiary amines such as cuprous chloride-triethylamine, cuproussulfatetributylamine, cuprous acetate-N- methylmorpholine and cuprouschloride-pyridine; catalysts comprising the combinations of cupricsalts, tertiary amines and alkali metal hydroxides such as cupricchloride-pyridinepotassium hydroxide cupric acetatetriethylaminesodiumhydroxide and cupric sulfate- N,N,N',N-tetramethylethylenediamine-potassium hydroxide; catalysts comprising thecombinations of cobalt salts and tertiary amines such as cobaltchloride-tributylamine and cobaltacetate-N,N,N',N'-tetramethy1ethylenediamine; catalysts comprising thecombinations of manganese salts and tertiary amines such as manganeseacetate-tributylamine and manganese acetylacetonatepyridine; catalystscomprising the combinations of manganese salts and alcohol amines suchas manganese acetate-ethanolamine, manganese stearatediethanolamine andmanganese acetylacetonate- ,B-hysuch as Q wQ H= N=o11 H2 Ha F l QF Q H=N=C )H Hz HZ Qf -Q H: 93 E 2):

and

OCHa CHaO JII=N" 1 m N=crt 2): 112);

The cocatalyst is selected from the group consisting of such transitionmetal compounds as cobaltous chloride, cobaltic chloride, nickelchloride, ferrous chloride, ferric chloride, cobaltous acetate, ferrousacetate, ferric acetate, cobaltous propionate, nickel benzoate,cobaltous nitrate, ferrous nitrate, cupric nitrate, Mn(CH- COCH COCHMn(CH COCH COCH Fe(CH- ,COCH COCH Fe(CH COCH- COCH Co(CH- .COCH COCHCo(CH COCH COCH- Ni(CH- COCH COCH Cu(CH COCH COCH and Zn(CHCOCHgCOCH3)g.

As the polymerization media, there are used those which dissolve the2,6-substituted phenols but do not dissolve polyphenylene ethers havinga specific viscosity 1; sp/c of not less than 0.25 among those obtainedby the polymerization. Another condition required for the media used inthe present invention is that they should be able to homogenouslydissolve oxidative polymerization catalysts for phenols. The media andcombinations thereof which are used in the present invention may beselected from an extremely wide scope. From the commercial standpoint,however, they are restricted in kind in consideration of such essentialsas cost and easiness of recovery thereof. The medium compoisitions usedin the present invention are limited to those which can givepolyphenylene ethers having molecular weights within a practical range.Among various combinations of media, there are some which cannot be putinto practical use because of their having no affinity for catalysts,even though they can sufficiently satisfy. with respect to solubilityfor monomers and polymers, conditions required for the media used in thepresent invention.

Examples of the media capable of being used alone includedimethylformamide, dimethylacetamide, trimethylene glycol, hexamethyleneglycol, dimethyl sulf- 4 oxide, hexamethyl phosphotriamide,methylethylketone, diethylketone, acetyl acetone, benzylmethylketone anddiethyl carbonate.

As the media to be used in the form of mixtures, there are used mixturesof solvents for the polymers with non-solvents for the polyers. Examplesof the former solvents include benzene, toluene, xylene, chlorobenzene,dichlorobenzene, nitrobenzene, ethylbenzene, styrene, methylstyrene,dimethylstyrene, chlorostyrene, methylene dichloride, chloroform,dichloroethylene, trichloroethane, bromoform, benzontrile, furan,thiophene, cyclopentanone and cyclohexanone, Examples of thenon-solvents for the polyers incude methanol, ethanol, n-propanol,iso-propanol, nbutanol, iso-butanol, tert-butanol, n-hexanol, nheptanol,benzyl alcohol, cyclopentanol, cyclohexanol, water, acetonitrile,propionitrile, acrylonitrile, diethyl ether, tetrahydrofuran, pentane,n-hexane, 2- methylpentane, n-heptane, n-ocatane, iso-octane,cyclopentane, cyclohexane, dimethylformamide, dimethylacetamide,trimethylene glycol, hexamethylene glycol, dimethylacetamide,trimethylene glycol, hexamethylene glycol, dimethylsulfoxide, hexamethylphosphotriamide, methylethylketone, diethylketone, acetylacetone,benzylmethylketone and diethyl carbonate.

ln a case of mixture, the ratio between the solvents to the non-solventsis selected from the range of (9 to 1) to (l to 9) by volume, takinginto an account of molecular weight of the final polymer and stabilityof slurry obtained. If the solvent is more than 9 to l, slurry is notsatisfactory, and if the solvent is less than 1 to 9, it makes nosubstantial difference from using the nonsolvents alone.

As the molecular oxygen-containing gas, there is used oxygen gas whichmay contain such inert gases as N and the like. Air may also be used.

B. Process B-l. First step A solution of 2,6-disubstituted phenol in theaforesaid solution is subjected to oxidative polymerization in a firstpolymerizer, while introducing a molecular oxygen-containing gas andwhile maintaining the solution state, until the conversion becomes 50 toThat is, in the first polymerizer, the flow rate of oxygencontaining gasand the average staying time are suitably controlled so that theconversion is maintained within the range from 50 to 95 and noprecipitate is deposited at all. At the same time, the heat ofpolymerization is sufficiently removed, taking advantage of the factthat the reaction system is a homogeneous solution. As the polymerizer,a complete mixing type polymerizer is used.

Since the oxidative polymerization reaction of phenol is a reaction inwhich the efficiency of contact of l the phenol with oxygen gas is to beenhanced, sufficient stirring should be made in the reactor. That is, apolymerizer in which no stirring takes place in the direction ofprogress of the reaction liquid is not suitable in the case of handlinga reaction mixture of such a low viscosity as in the present reaction.

In the present invention, the concentration of 2,6- disubstituted phenolis in the range from 15 to 35 by weight, preferably from 18 to 33 7: byweight. In order to obtain continuously a desirable slurry according tothe present process, the monomer concentration should be at least 15 byweight. If the monomer concentration is lower than 15 by weight,particles ofthe taining the conversion within the range ff6rif50% Theoxidative polymerization of 2,6-

to 95%. disubstituted pehnol is an extremely great exothermic reaction,so that the heat of polymerization should sufficiently be removed. Thatis, in the first step, such a major portion of the reaction as in therange from 50 to 95 is effected, and the heat of polymerization issufficiently removed, taking advantage of the fact that the reactionsystem is in a homogeneous solution state. If the reaetion liquid, whichis in such a state that the conversion is less than 50%, is transferredto a polymerizer for depositing polymer particles to the form of aslurry, there are undesirably brought about such drawbacks that thedeposited particles-are made unstable or a major portion of the reactionheat should be removed in the presence of slurry particles. If thereaction liquid is stayed in the first polymerizer until the conversionreaches more than 95 it becomes difficult to so control the reactionthat the reaction liquid can be sent to the second polymerizer prior tothe deposition to polymer particles.

Conditions for practicing the continuous polymeriza tion reaction of thepresent invention are decided by investigating the optimum conditions ofeach factor so that the reactor can successfully play its role. Thereaction temperature is selected from the range of 0 to 100C, preferably20 to 70C. The average staying time of reaction liquid in the reactor isselected from the range of 15 minutes to 7 hours, preferably 30 minutesto 4 hours.

The feeding of oxygen gas to the reactor is an impor tant factor for thecontrol of reaction. The present polymerization proceeds as much as anamount of oxygen absorbed. Oxygen is fed in the first step so that anamount of oxygen to be absorbed is 50 to 95 based on 2,6-disubstitutedphenol in order to control the conversion to 50 to 95 The presentinvention is enhanced if a solvent or nonsolvent for polyphenylene etheror a mixture of said two solvents is added to the reaction system duringthe course of polymerization.

B-2. Second step The reaction liquid, which has completed thepolymerization in the first step, is sent by means of the head pressureinto a second polymerizer. In the second polymerizer, the polymerizationis completed while depositing polymer particles. The deposited polymerparticles are prevented from adhesion to the reactor wall, stirringblades, etc. by the composition of medium, i.e. the combination of asolvent and a non-solvent and the quantitative ratio of the twosolvents. For this purpose, a solvent or non-solvent for polyphenyleneether, or a mixture of said solvents, may be added. The size andhardness of the polymer particles can be controlled by maintaining thestirring conditions at the range of 10 to 500 r.p.m., depending uponparticle size and hardness of precipitates. Oxygen may be fed in excess.The reaction temperature is from 0 to 100C., preferably from 20 to C.,and the average staying time is from 15 minutes to 7 hours, preferablyfrom 30 minutes to 4 hours. B-3. Third step In order to impart asuitable hardness to the polymer particles, there is sometimes used athird polymerizer as an aging tank. In this third polymerizer, thestirring conditions and the staying time are controlled so that thestirring is effected in 5 to 100 r.p.m., and the average staying time islO minutes to 10 hours, observing whether the desired slurry is obtainedor not. C. Product The polymer obtained in the above manner has aparticle size of 5to 500 microns and is stable.

The present invention is illustrated in further detail below withreference to examples, in which all parts are by weight.

Example 1 A mixed liquid comprising 500 parts of 2,6- dimethylphenol,127 parts of chloroform and 900 parts of toluene was fed at a rate of4.6 liters/hr. by use of a metering pump to a first reactor of 3 litersin volume. Separately, a solution in 440 parts of methanol of 3 parts ofcobaltous chloride, 10 parts of ethylenediamine and 20 parts ofsalicylaldehyde was fed to the first reactor at a rate of 1.4 liters/hr.by use of another metering pump. Into the first reactor, oxygen gas wasintroduced at a rate of 3.2 liters/min, and the inner temperature of thereactor was controlled to 25C, under stirring (40 r.p.m.). Staying timewas about 30 minutes. A homogeneous solution, which had left the firstreactor, was sent by means of the head pressure to a second reactor of 8liters in volume. Into the second reactor, oxygen gas was introduced ata rate of 1.0 li ter/min, while maintaining the inner temperature at 35Cand while vigorously stirring the solution at 300 r.p.m. Polymerparticles initiated to deposit in the second reactor, but were uniformlydistributed within the whole reactor by stirring. The reaction liquidcontaining the polymer particles was overflowed from the second reactorand then transferred to a third reactor of 8 liters in volume. Into thisreactor, oxygen gas was flowed at a rate of 0.3 liter/min. whilestirring the reaction liquid at r.p.m. The reaction liquid containingthe polymer particles was continuously overfiowed from the thirdreactor, and the then continuously subjected to filtration, washing anddrying to obtain poly- (2,6-dimethylphenylenel,4-ether) as whiteparticles. The thus obtained polymer particles were stable particleshaving diameters distributed within the range from 20 to 50 u. Theintrinsic viscosity '1 sp/c of the polymer measured in 0.5 chloroform at25C. was in the range of 0.62 i 0.02, and the operation could beeffected stably over a long period of time.

Example 2 A mixed liquid comprising 500 parts of 2-methyl-6-ethylphenol, 740 parts of n-propanol and 1,240 parts of xylene was fedat a rate of 4.9 liters/hr. by use of a metering pump to a first reactorof 3 liters in volume. Separately, a solution of 4 parts of cuprousacetate and 25 parts of tri(n-butyl)amine in 490 parts of chloroform wasfed to the first reactor at a rate of 1.1 liters/hr. by use of anothermetering pump. Into the first reactor, oxygen gas was flowed at a rateof 2.3 liters/min, and the inner temperature of the reactor wascontrolled to 30C, under stirring. A homogeneous solution, which hadleft the first reactor, was sent by means of the head pressure to asecond reactor of 8 liters in volume. Into the second reactor, oxygengas was flowed at a rate of 0.8 liter/min., while maintaining the innertemperature at 40C. and while vigorously stirring the solution at 240rpm. Polymer particles initiated to deposit in the second reactor, butwere uniformly distributed within the whole reactor by stirring.Thereafter, the same treatments as in Example 1 were repeated to obtainpoly( 2-methyl-6-ethylpheny1ene-1,4-ether) as white particles. The thusobtainted polymer particles were stable particles having diametersdistributed within the range from to 30 u. The intrinsic viscosity nsp/cof the polymer measured in 0.5 chloroform at 25C. was in the range of0.44 i 0.02, and the operation could be effected stably over a longperiod of time.

Example 3 A mixed liquid comprising 450 parts of 2,6- dimethylphenol,150 parts of n-butanol and 1,080 of ethylbenzene was fed at a rate of8.4 liters/hr. by use of a metering pump to a first reactor of 3 litersin volume. Separately, a solution of 11 parts of a cobalt chelaterepresented by the formula,

CHz--( JH2 and 9 parts of Cu(CH COCl-l CHCl-l in 300 parts of methanolwas fed to the first reaction at a rate of 0.6 liter/hr. by use ofanother metering pump. Into the first reactor, oxygen gas was flowed ata rate of 2.0 liters/- min., and the inner temperature of the reactorwas controlled to 25C, under stirring. A homogeneous solution, which hadleft the first reactor, was sent by means of the head pressure into asecond reactor of S liters in volume. Into the second reactor, oxygengas was flowed at a rate of 0.6 liters/min. while maintaining the innertemperature at 80C. and while vigorously stirring the solution at 350r.p.m. Thereafter, the same treatments as in Example 1 were effected toobtain poly(2,6-dimethylphenylene-1,4-ether) as white particles. Thepolymer particules were stable particles having diameters distributedwithin the range from 25 to 30 ,u.. The intrinsic viscosity nsp/c of thepolymer measured in 0.5 chloroform at 25C. was in the range of 0.71 i0.01, and the operation could be effected stably over a long period oftime.

Example 4 A mixed liquid comprising 330 parts of 2,6- dimethylphenol,130 parts of dichloroethylene and 810 parts of benzene was fed at a rateof 3.1 liters/hr. by use of a metering pump to a first reactor of 3liters in volume. Separately, a solution of 5 parts of cuprous chlorideand 30 parts of pyridine in a mixed solvent composed of 65 parts ofmethanol and 130 parts of npropanol was fed to the first reactor at arate of 0.9 1iter/hr. by use of another metering pump. Into the firstreactor, oxygen gas was flowed at a rate of 3.5 liters/- min., and theinner temperature of the reactor was controlled to 40C, under stirring.A homogenous solution, which had left in the first reactor, was sent bymeans of the head pressure to a second reactor of 8 liters in volume.Into the second reactor, oxygen gas was flowed at a rate of 1.0liter/min., while maintaining the inner temperature at 50C. and whilevigorously stirring the solution at 250 r.p.m. Polymer particlesinitiated to deposit in the second reactor, but were uniformlydistributed within the whole reactor by stirring. The reaction liquidcontaining the polymer particles was overflowed from the second reactor,and then transferred to a third reactor of 8 liters in volume which hadbeen kept at 30 C. Trito the third reactor, oxygen gas was flowed at arate of 0.2 liter/min. While stirring the reaction liquid at 40 r.p.m.The reaction liquid containing the polymer particles was continuouslyoverflowed from the third reactor, and then continuously subjected tofiltration, washing and drying to obtain poly(2,6-dimethylphenylene-l,4-ether) as white particles. The thus obtainedpolymer particles were stable particles having diameters distributedwithin the range from 20 to 40 u. The intrinsic viscosity nsp/c of thepolymer measured in 0.5 chloroform at 25C. was in the range of 0.77 i0.03, and the operation could be effected stably over a long period oftime.

Example 5 A mixed liquid comprising 600 parts of2-ethyl-6-npropylphenol, 300 parts of acetonitrile and 1,100 parts ofdimethylstyrene was fed at a rate of 4.9 liters/hr. by use of a meteringpump to a first reactor of 3 liters in volume. Separately, a solution of5 parts of manganese acetate, 20 parts of tri(n-butyl)-amine,ancl 5parts of sodium methoxide in a mixed solvent composed of 200 parts ofdiethyl carbonate and 270 parts of ethanol was fed to the first reactorat a rate of 1.1 liters/hr. by use of another metering pump. Into thefirst reactor, oxygen gas was flowed at a rate of 4.0 liters/min., andthe inner temperature of the reactor was controled to 35C, understirring. A homogeneous solution, which had left the first reactor, wassent by'means of the head pressure to a second reactor of 8 liters involume. Intothe second reactor, oxygen gas was flowed at a rate of 1.2liters/min., while maintaining the inner temperature at 45C. and whilevigorously stirring the solution at 400 r.p.m. Thereafter, the sametreatments as in Example 1 were effected to obtainp0ly(2-ethyl-6-npropylphenylene-l,4-ether) as white crystals. The thusobtained polymer particles were stable particles having diametersdistributed within the range from 40 to, ,u. The intrinsic viscosity'nsp/c of the polymer measured in 0.5 chloroform at 25C. was in therange of 0.51 i 0.02, and the operation could be effected stably over along period of time.

Example 6 A mixed liquid comprising 700 parts of 2,6- dimethylphenol,300 parts of propionitrile and 700 parts of mixed xylene was fed at arate of 6.8 liters/hr. by use of a metering pump to a first reactor of 5liters in volume. Separately, a solution of 6 parts of cupric acetate,15 parts of triethylamine and 10 parts of potassium hydroxide in a mixedsolvent composed of 260 parts of chloroform and 510parts of isopropanolwas fed to the first reactor at a rate of 3.2 liters/hr. by use ofanother metering pump. Into the first reactor, oxygen gas was flowed ata rate of 7.0 liters/min, and the inner temperature of the reactor wascontrolled to 30C, under stirring. A homogeneous solution, which hadleft the first reactor, was sent by means of the head pressure to asecond reactor of 2.0 liters in volume. Into the second reactor, oxygengas was flowed at a rate of 1.0 liter/min, while maintaining the innertemperature at 40C. and while vigorously stirring the solution at 300r.p.m. Polymer particles initiated to deposit in the second reactor, butwere uniformly distributed within the whole reactor by stirring. Thereaction liquid containing the polymer particles was continuouslyoverflowed from the second reactor, and then continuously subjected tofiltration, washing and drying to obtainpoly(2,6-dimethylphenylene-l,4-ether) as white particles. The thusobtained polymer particles were stable particles having diametersdistributed within the range from to 70 ,u.. The intrinsic viscositynsp/c of the polymer measured in 0.5 chloroform at 25C. was in the rangeof 0.66 i 0.05, and the operation could be effected stably over a longperiod of time.

We claim:

1. A process for producing polyphenylene ethers which comprises a firststep of passing a molecular oxygen-containing gas in the presence ofacatalyst into a solution of a 2,6-disubstituted phenol having theformula where R is a straight chain alkyl group having one to fourcarbon atoms and R is a halogen atom, a n-alkoxy group having one tofour carbon atoms or an n-alkyl group having one to four carbon atoms ina medium capable of dissolving the catalyst as well as the 2,6-disubstituted phenol but incapable of dissolving a polyphenylene etherhaving a specific viscosity of not less than 0.25, the amount of said2,6 -disubstituted phenol being to 35 by weight based on the totalweight of the polymerization liquid, and keeping the polymerizationliquid at a temperature of Oto l00C., while stirring and preventing theliquid from formation of precipitate, until 50 to 95 of the2,6-disubstituted phenol is polymerized; and a second step oftransferring the reaction liquid in the form ofa solution to anotherreaction zone, into which the oxygen-containing gas is introduced, whilestirring the liquid and allowing the precipitation of polyphenyleneether at a temperature of 0 to 100C., to complete the polymerization ofthe 2,6-disubstituted phenol.

2. A process according to claim 1 wherein the 2,6- disubstituted phenolis 2,6-dimethylphenol or 2,6- diethylphenol.

3. A process according to claim 1, wherein the medium is one memberselected from the group consisting of dimethylformamide,dimethylacetamide, trimethylene glycol, hexamethylene glycol, dimethylsulfoxide, hexamethyl phosphotriamide, methylethylketone, diethylketone,acetylacetone, benzylmethylketone and diethyl carbonate.

4. A process according to claim 1, wherein the medium is a mixture of atleast one member selected from the group consisting of benzene, toluene,xylene, chlorobenzene, dichlorobenzene, nitrobenzene, ethylbenzene,styrene, methylstyrene, chlorostyrene, dimethylstyrene, methylenedichloride, chloroform, dichloroethylene, trichloroethylene, bromoform,benzonitrile, furan, thiophene, cyclopentanone and cyclohexanone, withat least one member selected from the group consisting of methanol,ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol,n-hexanol, nheptanol, benzyl alcohol, cyclopentanol, cyclohexanol,water, acetonitrile, propionitrile, acrylonitrile, diethyl ether,tetrahydrofuran, pentane, n-hexane, 2- methylpentane, n-heptane,n-octane, iso-octane, cyclopentane, cyclohexane, dimethylformamide,dimethylacetamide, trimethylene glycol, hexamethylene glycol, dimethylsulfoxide, hexamethyl phosphotriamide, methylethylketone, diethylketone,acetylacetone, benzylmethylketone and diethyl carbonate.

5. A process according to claim 1, wherein the reaction temperatures inboth the first and second steps are individually 20 to C.

6. A process according to claim 1, wherein the average staying times inboth the first and second steps are individually 15 minutes to 7 hours.

7. A process according to claim 1, wherein the average staying times inboth the first and second steps are individually 30 minutes to 4 hours.

8. A process according to claim 1, wherein the first step is carried outwhile removing the heat of polymerization as much as possible.

9. A process according to claim 1, wherein the reaction liquid isfurther subjected to a third step for aging.

10. A process according to claim 1, wherein each step is subdivided intotwo or more steps.

2. A process according to claim 1 wherein the 2,6-disubstituted phenolis 2,6-dimethylphenol or 2,6-diethylphenol.
 3. A process according toclaim 1, wherein the medium is one member selected from the groupconsisting of dimethylformamide, dimethylacetamide, trimethylene glycol,hexamethylene glycol, dimethyl sulfoxide, hexamethyl phosphotriamide,methylethylketone, diethylketone, acetylacetone, benzylmethylketone anddiethyl carbonate.
 4. A process according to claim 1, wherein the mediumis a mixture of at least one member selected from the group consistingof benzene, toluene, xylene, chlorobenzene, dichlorobenzene,nitrobenzene, ethylbenzene, styrene, methylstyrene, chlorostyrene,dimethylstyrene, methylene dichloride, chloroform, dichloroethylene,trichloroethylene, bromoform, benzonitrile, furan, thiophene,cyclopentanone and cyclohexanone, with at least one member selected fromthe group consisting of methanol, ethanol, n-propanol, isopropanol,n-butanol, isobutanol, tert-butanol, n-hexanol, n-heptanol, benzylalcohol, cyclopentanol, cyclohexanol, water, acetonitrile,propionitrile, acrylonitrile, diethyl ether, tetrahydrofuran, pentane,n-hexane, 2-methylpentane, n-heptane, n-octane, iso-octane,cyclopentane, cyclohexane, dimethylformamide, dimethylacetamide,trimethylene glycol, hexamethylene glycol, dimethyl sulfoxide,hexamethyl phosphotriamide, methylethylketone, diethylketone,acetyLacetone, benzylmethylketone and diethyl carbonate.
 5. A processaccording to claim 1, wherein the reaction temperatures in both thefirst and second steps are individually 20* to 70*C.
 6. A processaccording to claim 1, wherein the average staying times in both thefirst and second steps are individually 15 minutes to 7 hours.
 7. Aprocess according to claim 1, wherein the average staying times in boththe first and second steps are individually 30 minutes to 4 hours.
 8. Aprocess according to claim 1, wherein the first step is carried outwhile removing the heat of polymerization as much as possible.
 9. Aprocess according to claim 1, wherein the reaction liquid is furthersubjected to a third step for aging.
 10. A process according to claim 1,wherein each step is subdivided into two or more steps.